1. Field of the Invention
The present invention relates generally to a resistor, and more specifically to an embedded resistor.
2. Description of the Prior Art
In a semiconductor process, semiconductor materials, such as polysilicon, are often positioned to function as resistors capable of providing high resistance. These resistors can be used in place of load transistors. When load transistors of a static random access memory (SRAM) are replaced by semiconductor resistors, the number of transistors in the SRAM can be reduced thereby saving costs and enhancing the integration of the SRAM.
Conventionally used semiconductor resistors can be divided into polysilicon resistors and diffusion resistors. A polysilicon resistor is formed, for example, by forming a polysilicon film into which dopants are doped through an insulating film on a semiconductor substrate. The resistance of the polysilicon resistor can be controlled by the dopant concentration of the polysilicon layer. A diffusion resistor is formed, for example, by doping dopants into a semiconductor substrate to form a diffusion layer, and then by using a thermal diffusion method to activate the dopants in the diffusion layer and adjust the resistance thereof. Normally, whether it is a polysilicon resistor or a diffusion resistor, the resistor has a sandwich-like structure that sandwiches a high resistance region between two low resistance ends. The low resistance ends are provided for forming interconnection contact plugs to connect the resistor with other wirings. The high resistance region is used to provide a high resistance to satisfy circuit designs or device demands.
With the development of the various and miniaturized electronic products, circuit designs applying load resistors become more and more complicated, and requirements in volume, position and high resistance of the load resistors therefore become more and more critical as well.